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' 1444 MARIPOSA ROAD WKA No 2938 06 September 6, 2000 Page 3 samples were obtained from the sidewalls and bottom of the excavation Laboratory test results ' for the sidewall samples, obtained from a depth of approximately 22 feet, revealed non- detectable concentrations of Total Petroleum Hydrocarbons(TPH) as gasoline, diesel, and motor ' oil and non-detectable concentrations of Benzene, Toluene, Ethylbenzene, and Total Xylenes (BTEX) Results for the bottom samples, obtained from depths of 27 to 30 feet,revealed TPH as ' gasoline concentrations ranging from non-detectable to 25,000 mg/kg Based on these results, the excavation was deepened to approximately 36 feet below grade on November 9, 1992 ' At approximately 36 feet below surface grade,petroleum hydrocarbon odors were still noticeable in the soils, so an exploratory trench was constructed in the center of the excavation to a depth of ' approximately 44 feet below surface grade Soil sample EX11-44' was obtained at the bottom of the exploratory trench Results of laboratory analysis revealed detectable concentrations of TPH ' as gasoline (6,800 mg/kg),benzene (95 mg/kg),toluene (550 mg/kg), and total xylenes (670 mg/kg) Because further excavation would require sloping of the sidewalls, the decision was made to drill exploratory soil borings to further evaluate the vertical and lateral extentl of hydrocarbon contamination Soil Borings ' From March 29, 1993 to March 31, 1993, four soil borings (Bi through B4)were drilled in the immediate vicinity of the UST excavation Boring Bl was constructed approximately,five feet easterly of the excavation and extended to a depth of 86 5 feet Drilling was discontinued when groundwater was encountered in the boring at a depth of approximately 85 feet. Soil borings B2 and B3 were drilled at approximate 30° angles from vertical beneath the location ' of former underground storage tanks to vertical depths of 71 and 81 feet below site grade The soils in these borings consisted primarily of silty clays and clayey silts, two thin sand layers were observed at depths of approximately 49 to 53 feet and 63 to 68 feet Boring B4 was constructed approximately ten feet westerly of the excavation to a depth of 49 5 feet A slight petroleum odor was noted in each of the four soil borings Analytical results of selected soil samples from ' the four soil borings revealed relatively low concentrations of petroleum constituents at a depth . of 75 feet below surface grade WALLACE KUHL Recycled paper &ASSOCIATES INC